A chemical analysis device, such as a gas or liquid chromatograph, is a complex instrument that generally includes a computer (or control portion), a number of inlets and fluid paths, and one or more detectors. The control portion is typically coupled to the detectors and to pneumatic control electronics through a multi-conductor cable. The multiple conductors in the cable are used to supply power, ground, timing, and a number of different control and data signals. Typically, the cable includes forty or more conductors. Because such a cable is required for each detector, or other peripheral device, the chromatograph is typically limited to a fixed number of connection points for detectors and peripheral devices. Further, it is common to use a printed circuit (PC) board to PC board connection between the control electronics and the detector, thus requiring a fixed spatial relationship between the control electronics and the detector.
There are many events that occur in a chromatograph that require signal timing alignment between and among the control electronics, detectors and peripheral devices. For example, the timing of the generation of a detector signal depends on other processes occurring in the chromatograph, such as injection time and temperature control. Accordingly, the control electronics typically includes a master timing reference, referred to as a master clock. All runtime events in the chromatograph should occur relative to the master clock signal. For example, the control signal used to initiate the analog-to-digital conversion in the detector must be sent to each detector at a precise time. Unfortunately, this requires a separate conductor for each detector.
Advances in connection architecture for the components of a chromatograph use fewer conductors than in previous arrangements. Such an architecture makes use of multiplexing technology to place multiple control signals on two conductors using a bi-directional differential serial communication methodology. Such architecture minimizes the number of conductors in the interconnect cable and also facilitates expansion and system flexibility by eliminating the PC board-to-PC board connection of previous systems. However, the use of a bi-directional differential serial communication methodology creates timing synchronization difficulties because dedicated conductors are not available to allow the timing elements in the peripheral modules to synchronize with the master clock.
Therefore, it would be desirable to have the ability to synchronize multiple peripheral devices with a master clock using a differential serial communication methodology.